The invention relates to an inverted current rectifier with self commutation which is suitable for drives with one or more asynchronous and synchronous motors, in addition to other types of load impedances.
A number of inverted current rectifiers are known where problems of the self commutation of the rectifier and of accumulation of power in load inductances are solved. A rather progressive and perspective method is the so-called three-stage commutation of inverted current rectifiers wherein the disconnection of thyristors of the inverted rectifier and the current commutation in the phase are separated. There is, however, a problem with accumulation of power, which has to be, with smallest possible losses, discharged from the capacitors of the inverted rectifier in order to obtain an equilibrium. This problem leads to different solutions for inverted rectifiers of large output and inverted rectifiers of small output. Due to the complexity of the power part and of the regulation part, solutions, as for instance the inverting of accumulated power from DC capacitors in the inverted rectifier to the supply network, are unsuitable for inverted rectifiers of smaller and medium output. On the other hand solutions using the simplest means for discharge of the accumulated power by a parallel resistance represent substantial losses. Another problem of inverted current rectifiers with two-stage and three-stage commutation is the problem of breakdown conditions which may occur on the load (short circuits, disconnection of the load) or directly in the rectifier (parasite pulses on thyristors, failures of the regulating circuit and others). Some of these failures have the characteristic of random processes (for instant parasite pulses caused by transient processes in other electrical arrangements) and it is rather desirable that the inverted rectifier should maintain its function without the reaction of protective circuits. For industrial applications of drives of demanding operations a thus solved question of reliability in the conception of power circuits of the inverted rectifier is rather desirable.